Questions and Answers
The sound velocity in water is approximately ______ mm per µSec.
1.5
The Total Window Length (TWL) is set at ______ µSec.
40
To avoid triggering on serial data, the holdoff is calculated as ______ µSec.
162
For a 6" pipe, the calculated delay is ______ µSec.
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The maximum rep-rate can be determined by adding the delay to TWL and minimum time, resulting in ______ µSec.
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The inner radius (IR) is measured from the mirror to the ______ with a speed of 1480 m/s.
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The wall thickness (WT) is the distance from the inner wall to the ______, traveling at 5960 m/s.
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The Offset Trigger Delay (OTD) is denoted as ______.
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The length of the second window (L2nd W) is indicated as ______.
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The total window (TW) is labeled with the number ______.
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Study Notes
Key Parameters and Abbreviations
- 1 inch is approximately 25 mm (more precisely 25.4 mm).
- Sound velocity in steel is around 5960 m/s (or approximately 6 mm per µSec).
- Sound velocity in water is about 1480 m/s (or approximately 1.5 mm per µSec).
- Total Window Length (TWL) is 40 µSec.
- Backwall (BW) occurs at 50% of Total Window Length.
- Start of the second window (2nd W) is set at 1.0 µSec.
- Backwall for the second window is at 50% of this window.
- Offset Trigger Delay (OTD) for a standard Ultrasonic Testing (UT) head is 40 µSec.
- Minimum time between end of the Total Window (ETW) and the next Initial Pulse (NIP) is 70 µSec.
- Holdoff is defined as rep-rate (in µSec) minus 70 µSec for avoiding triggering on serial data.
Example Calculation for 6" Pipe with Wall Thickness of 7.1 mm
- For a 6" pipe, the diameter in mm is 150 mm, leading to a calculated delay of 100 µSec:
((150 / 2) x 2 / 1.5 = 100 µSec). - The calculated time for wall thickness (WT) of 7.1 mm results in approximately 2.4 µSec:
((7.1 x 2) / 6 = 2.4 µSec).
Delay Calculation
- Delay is found by adding OTD, Inner Radius (IR), and WT, then subtracting half of TWL:
[40 + 100 + 2.4 - 20 = 122.4 µSec]
Maximum Rep-Rate Calculation
- Maximum rep-rate is calculated as delay plus TWL and minimum time:
[122 + 40 + 70 = 232 µSec], equating to approximately 4310 measurements per second.
Holdoff Calculation
- Holdoff is determined by subtracting 70 µSec from the time between Initial Pulse (IP) to NIP:
[232 - 70 = 162 µSec].
Second Window Length Calculation
- The second window length is calculated using:
[(WT - Start of 2nd W) x 2 = (2.4 - 1.0) x 2 = 2.8 µSec].
Practical Considerations
- These calculations serve as a fast guide for approximate settings without a calculator but require fine-tuning for real-world applications.
- The maximum rep-rate is influenced not just by the timing but also by the motor's maximum speed, which can reach about 25 times for DC motors and 13 times for stepper motors.
- The measurement per revolution can be derived by dividing the rep-rate by the motor speed.
Diagram Elements
- The calculation diagram illustrates various components and measurements such as Offset Trigger Delay, Inner Radius, Total Window, and distances involved between the transducer, inner wall, and backwalls related to measurements.
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Description
Test your understanding of key parameters and calculations used in ultrasonic testing. This quiz covers sound velocity in materials, window lengths, and delay calculations for pipe wall thickness. Ideal for students and professionals in nondestructive testing (NDT).
